June 2015:

Our first clue that something was amiss, though, came one morning in the spring of 2015 when we found the feeder pole bent and the two large feeders empty on the ground.  We suspected that raccoons were the culprits.

Following advice found on the web, we began bringing the feeders in at dusk which temporarily solved the problem.

However, after several weeks we came out just before sunset to find the feeders intact but empty - this happened again and we started checking the feeders every few minutes in late afternoon.

We soon discovered that our raccoon had successfully changed his strategy to arrive several hours before we took in the feeders.

His rewards for solving this round of the T&E challenge was a free seat on the squirrel dome and access to an all-you-can-eat sunflower seed buffet.

Not one to forfeit the contest to a critter without a fight, I started looking around for a solution that would keep the raccoons completely off of the feeder.

There were several metal raccoon shields available for sale on the Internet, but I wanted to see if I could win the battle of wits with on-hand materials.

We had several old flimsy plastic flower pots, and I figured that if the sides were slick enough to keep raccoon claws from gaining a foothold and tall enough to keep the raccoon's front paws from grabbing the bottom of the feeder and hauling himself up I might just have a solution.

However, this was a determined raccoon on a mission, and he quickly found his way to a nearby feeder where he successfully employed the squirrel shield bypass maneuver and started emptying the new feeders.

Fortunately I had another pot available, and about 15 minutes of work successfully prevented the raccoon from returning to the other feeder.

July, 2015 update:

After about a month there are still no raccoon issues with either feeder station even though we now keep the feeders out all  night with the pot shields in place. 

One deficiency of T&E problem solving, however, is that because the goal is usually a solution to a single immediate problem, other consequences of an apparently successful resolution might not be apparent.

In this case, almost immediately after the raccoon visits had been discouraged the feeders were again quickly emptied during midday.  We initially thought the raccoon was back even earlier in the day, and we started watching again.

This time we discovered that the flat top of the pot provided a perch for magpies (that had never before shown an interest in the feeders) to stand comfortably and pull seed out of the feeders at blinding speed. 

A quick and easy T&E fix that seems to be working so far was to place a strip of duct tape over the feeder holes that face the pot top so the magpies can't reach the seed until they figure out how to rip off the tape - fortunately they choose not to sit on the relatively small feeder perches.

August 2015 update:

Apparently a larger raccoon moved into the neighborhood during the summer because the feeders started emptying overnight again.

From studying the earlier pictures it appeared that in order to reach the feeder, the raccoon had to grip the main pole with one hand while reaching up and around with the other arm. 
(Raccoons: It's All In The Hands)

I figured that if I could prevent the raccoon from gripping the pole by increasing the diameter there would be no way it could maintain a grip while reaching up and around to the feeders.  I slid a 3.5 inch PVC pipe over the pole that reached from the ground to the inside bottom of the inverted pot. 

September 2015 update:

There has been no evidence for over a month that  the raccoons have figured out how to get on top of the pot and access the seed. 

There have been dirt streaks on the white PVC pipe, however, that suggest the raccoons can shimmy up the pipe by hugging it with both arms.  But they slide down when they let go with one arm to reach around to the feeder.  We have not yet been able to witness their attempts at accessing the food with the PVC pipe in place.

October 2015 update:

Sigh!